Just this past tuesday we started experiencing a problem with some of the hosts on our server. At this time we are not sure how wide spread the problem is but we know at least a few of the sites are having issues.

The problem is that transfer rates on the upload are horrid. Upload on ftp for affected domains is less than 20kbps. Try and send an email attachment through an affected IP? Forget about it! It will time out completely!

Then there are the other hosts on the same server that work perfectly!

Is the problem intermittent or readily reproducible? Have you done any pings or traceroutes when encountering the issue? Have you checked autonegotiation/duplex settings on your NICs? How long had the box been up previously without this error (new server?)?